The prsent invention relates to an electrophotographic apparatus and an electrophotographic process, using a photoreceptor having a photoconductive layer made of an amorphous silicon, and imparting pressure to a photoreceptor for conducting transference or simultaneous transference and fixation of a toner image onto a transfer paper.
For electrophotography, a so-called Carlson process of using a photoreceptor and comprising steps of electric charging, exposure, development, transference, cleaning and discharging has widely been employed. In accordance with the process, a toner image as developed is transferred to a transfer paper and then fixed thereon by a thermal roll system or pressure fixation system to obtain a final image.
As a transferring means in the process, generally used is a corotron. However, where the transference is effected with a corotron in the process, the toner being used would scatter during transference so that an image of high quality could hardly be obtained.
Simultaneous transference and fixation has been proposed for simplifying the process. As one example of using an amorphous silicon photoreceptor, JP-A 55-87156 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") has proposed a method of simultaneous transference and fixation of a toner image onto a transfer paper with a hot fixing roller, using an amorphous silicon photoreceptor. In accordance with the method, however, since the surface of the roller is heated up to a high temperature of 180.degree. C., continuous contact of the roller with the photoreceptor is impossible and a device of cooling the photoreceptor is necessary. Thus, the method involves some problems that it needs a complicated mechanisms and is unsuitable to continuous use. JP-A 1-43954 has proposed a method of simultaneous transference and fixation of using an electroconductive one-component toner under pressure. In accordance with the method of effecting simultaneous transference and fixation with imparting pressure to the photoreceptor, however, in case that the device of imparting pressure to the photoreceptor is directly kept in contact with the photoreceptor, that is, in case that a transfer paper is not between the photoreceptor and the device of imparting pressure to the photoreceptor, the toner would be transferred and fixed onto the device of imparting pressure to the photoreceptor when even a slight toner image has been formed on the photoreceptor. The troublesome phenomenon causes staining of the inner parts of the apparatus, clogging of transfer papers in the apparatus and staining of the back surface of the transferred papers and, as a result, it noticeably lowers the reliability of duplication operation by the method.
In order to improve the electrophotographic characteristics of an amorphous silicon photoreceptor, provision of a surface layer on the photoreceptor has been proposed. The surface layer is desired to be thicker so as to improve the mechanical strength thereof. In general, however, since the layer is made of an insulator, it would have a high residual potential when it is thick. As a result, the high residual potential would promote developability to often cause generation of fog. Because of the reason, the surface layer is generally designed to have a thickness of approximately from 0.1 to 1 .mu.m and a residual potential of approximately from 0 to 50 volts.